S. J. Harrison

Experimental Study of Free Convection at an Indoor Glazing Surface with a Venetian Blind

A Mach-Zehnder interferometer was used to measure the laminar free convective heat transfer rate from an isothermal vertical surface adjacent to a set of aluminum Venetian blinds. Local and average heat transfer data were obtained at three different blind-to-plate spacings, and at four different blade angles. Data are presented up to a Rayleigh number of Ra =3 × 107, based on the distance from the leading edge. Flow visualization results that illustrate the cellular flow patterns between the blades are also presented. Overall, it was found that the flow field and local heat transfer distribution on the surface can be significantly affected by the presence a Venetian blind. When placed close to the surface, the blind causes a strong periodic variation in the local Nusselt number distribution. However, for all cases studied the average Nusselt number was within 13% of an isolated vertical flat plate at the same Rayleigh number.

Numerical Study of Convective and Radiative Heat Transfer from a Window Glazing with a Venetian Blind

A two-dimensional numerical solution has been obtained of the effect of a venetian blind on the conjugate heat transfer at an indoor window glazing. A solution has been obtained to the coupled laminar free convection and radiation heat transfer problem, including conduction along the blind slats. The local convective Nusselt number distributions were found to compare well with published experimental data for an aluminum blind. Also, there was good qualitative agreement with temperature and flow field visualization photographs. The results show that, over a wide range of Rayleigh numbers, an aluminum venetian blind can have a strong effect on the heat transfer rate from the indoor window glazing. Depending upon the specific conditions, the average convective heat transfer rate can either increase or decrease. However, for all cases studied, the blind was found to substantially reduce the radiative heat transfer rate from the window, even when the slats were fully open.

An Interferometric Study of Free Convection at a Window Glazing with a Heated Venetian Blind

The free convective heat transfer rate from a vertical isothermal plate adjacent to a heated aluminum venetian blind has been measured using a Mach-Zehnder interferometer. The blind was heated electrically to simulate solar heating, and the plate was heated above the room temperature to simulate an indoor window glazing. Local and average heat transfer data were obtained for three blind heat flux levels, two blind-to-plate spacings, and four slat angles in the laminar flow regime. For most cases, data were obtained up to a plate Rayleigh number of Ra L = 2.8 × 106 based on the distance from the leading edge. Infinite fringe interferograms were taken for temperature field visualization. The results show that blind heat flux has a strong influence on local and average heat transfer coefficients on the plate. It was also found that the spacing between the inner tips of the slats and the plate had a substantial impact on the convection. For close spacings, the heated slats were found to produce a strong periodic variation in the local heat transfer distribution on the plate. For all cases studied, as the blind heat flux increased, the convective heat transfer rate from the plate decreased dramatically. In addition, as the blind heat flux increased, the average convection coefficient became more dependent on both the blind-to-plate spacing and slat angle.

Heat Transfer From an Isothermal Vertical Surface With Adjacent Heated Horizontal Louvers: Validation

The present study examines the influence of heated, horizontal, and rotateable louvers on the convective heat transfer from a heated or cooled vertical isothermal surface. The system represents an irradiated Venetian blind adjacent to the indoor surface of a window. Detailed temperature field and local surface flux data were obtained using a Mach-Zehnder Interferometer for two window temperatures (warm and cool compared to ambient) and irradiation levels, two louver to plate spacings, and three louver angles. The results have been compared to a steady, laminar, two-dimensional, conjugate conduction/ convection/radiation finite element model of this problem

The Effect of Coverings on Heat Transfer from a Window to a Room

Abstract The presence of a blind adjacent to a window affects the natural convective and radiant heat transfer from the window to the room. As a result, the use of a shading device will change the heat transmission and solar heat gain through the window. A number of numerical and experimental studies of the effects of blinds on the heat transfer from a window have therefore been undertaken, with some of the main features of these studies being described here. In these studies, attention has been given to Venetian, vertical, and plane blinds, although the major attention has been given to Venetian blinds. Initial studies examined the effect of all three types of blinds on the natural convective heat transfer at an indoor glazing surface when there is no solar irradiance. Supporting experimental studies using mainly interferometry were then undertaken, particularly for the Venetian blind case. The numerical and experimental work was then extended to include the effects of solar radiation, in particular the effect of heat generation in the blind resulting from absorbed solar radiation. In addition to providing basic information on the effects of blinds on the heat transfer process, the studies described here will assist in expanding available software for predicting window heat transfer to include the effect of window coverings and assist in the selection of energy-efficient window coverings.

Heat Transfer From an Isothermal Vertical Surface With Adjacent Heated Horizontal Louvers: Numerical Analysis

The present study examines the influence of heated, horizontal, and rotatable louvers on the convective and radiative heat transfer from a heated or cooled vertical isothermal surface. The system represents an irradiated Venetian blind adjacent to the indoor surface of a window. Detailed heat transfer results were obtained using a steady, laminar, two-dimensional, conjugate conduction/convection/radiation finite element model for two window temperatures (warm and cool compared to ambient) and irradiation levels, two louver to surface spacings, and three louver angles. The effect of the heated louvers on the heat transfer rate from the surface has been demonstrated